1 ) A mountaineer shouts his name in valley . Half a sec later , he hears the echo . How far away is the rock which is reflecting his voice ?
A ) 80 m , B
) 86 m
,
C ) 82 m , D
) None of these ,
Correct
Answer : - B ) 86 m ,
Solution
: -
Given
data : -
· t = 0.5/2 sec = 0.25 sec ( we divide time by 2 because voice took 0.5 sec ( half sec ) for both going towards rock and reflecting
back to person . And we just have to
find distance between rock and person in
single direction ) ,
· Speed of sound in air = 343 m/s ,
· Distance = ?
( between rock and person ) .
Formula
: -
v =
d / t ,
Ø d = v
x t ,
Ø d =
343 x 0.25
Ø d = 85.75
m , Answer .
2 ) A
wire is bent into a ring of radius R and given a charge q . The magnitude of electric field at the center
of ring is ……. ,
A ) Infinite , B
) finite ,
C ) zero , D
) None of these ,
Correct
Answer : - C ) zero ,
3 )
The electric field due to an infinity long thin wire at a distance R varies as
……….. ( 1/R ) .
4 ) A particle is displaced from a position 2i - j + k to another position 3i - 2j
+2k under action of a force ( F = 2i - j
+ k ) . The work done by force is ?
A ) 2J , B
) 4J ,
C ) 8J , D
) None of these ,
Correct
Answer : - B ) 4J ,
Solution
: -
Given
data : -
F = 2i - j + k ,
d1 = 2i - j + k ,
d2 = 3i - 2j +2k ,
W = ?
Formula
: -
W =
F.d ,
d = d1 - d2 = ( 3 - 2 )i + ( -2 - (-1))j + ( 2 - 1
)k =
1i - 1j +1k ,
So ,
W = (2)(1) + (-1)(-1) + (1)(1) ,
W =
4J , Answer .
